Protective device in television receivers



Jan. 23, 1940. M, VON ARDENNE 2,188,290

PROTECTIVE DEVICE IN TELEVISION RECEIVERS Original Filed Nov. 13, 1933Jaye/Mar? Patented Jan. 23, 1940 UNITED STATES PATENT OFFICE PROTECTIVEDEVICE 1N TELEVISION RECEIVERS Manfred von Ardenne, Berlin, Germany 14,November 15, 1932 1 Claim.

The invention relates to the particular embodiment of mains apparatusfor delaying the initiation of the anode potential in Braun tubes. Theuse of indirectly heated cathodes in tube apparatus, in Braun tubes,acts detrimentally on the life thereof, owing to the long time requiredfor heating the cathode, if the full anode potential becomes efiectivebefore the cathode has attained a sufficiently high temperature. Nowwhen using normal mains apparatus the anode potential acquires its fullvoltage almost instantaneously, whereas the temperature of the cathode,and together therewith the emission, increases only very slowly, andfrequently does not attain a sufiiciently high value until after anelapse of several minutes.

This application is a division of application Serial No. 697,739, filedNovember 13, 1933, Patent No. 2,096,987, dated October 26, 1937.

In the interval before the complete emission takes place there isproduced a particularly strong cathode fall, which leads to a vigorousbombardment of ions and to a greatly shortened life and a deformation ofthe cathode, similar to the manner in which, as well known, under-heatedcathodes are subject to premature wear or damage in tube apparatus. Ifthe heating period amounts, for example, to 1 minute for an indirectlyheated cathode, the dangerous state with the bombardment of ionscommences, as experiments have shown, after approximately 10 seconds.

Said cathode fall is particularly dangerous because of the relativelysmall surface of the highly emissive material.

According to the invention, these disadvantages are overcome by specialmeasures preventing the anode D. C. potential from becoming its fullvalue before the cathode has reached a sufiiciently high temperature andaccordingly an adequate emission.

The present invention will be best understood by the accompanyingdrawing, in which I is the mains transformer, 2, 7 and I2 cathodefilament, Wehnelt cylinder and anode of a Braun tube, 5 a rectifier tubehaving a cathode filament 4 and anode 8. The transformer is providedwith three secondary windings of which 6 produces the high alternatingtension for the rectifier whilst the two other secondary windings areconnected to the heater of the Braun tube via an adjustable re- 1936,Serial No. 105,626. In Germany sistance 3, respectively to the filament4 of the rectifier tube 5 via a thermionic time lag device 15. The anodetube 5 is connected tothe Wehnelt cylinder 1 and via a biassingresistance 9 to the cathode 2. The condensers I 0 and II serve forsmoothing.

The use of such a time switch device is well known for other purposesfor example for limiting the anode current as shown by the Britishpatent specification No. 372,799.

The device l5 may consist, in a well known manner, of a thermic relayoperated, for example, by the heating current of the cathode of theBraun tube and actuates a switch closing the heating circuit of thecathode 4 after a certain ime.

The possible form of embodiment referred to may undergo numerousmodifications within the meaning of the invention. It is essential thatin each case a thermic time lag device is provided in order to ensurethat the anode potential does not reach its full value until after theelapse of a certain time which is necessary to raise the indirectlyheated cathode to a sufiiciently high temperature.

I claim:

In a television receiver a mains supply and a 9 Braun tube havingcathode filament, Wehnelt cylinder and anode, said mains supplycomprising a transformer having a primary winding connected to the mainsand three secondary windings, a rectifier tube producing the directcurrent high tension for the anode and the Wehnelt cylinder of saidBraun tube, and smoothing means, one of said secondary windingsconnected on the one side to the cathode of said rectifier and on theother side to the anode of said Braun tube, the second to the filamentof said Braun tube, the third to the filament of said rectifier tube, inthe last circuit a thermostatic switch closing the circuit after acertain time interval the anode of said rectifier being connecteddirectly to said Wehnelt cylinder and via a resistance to said cathodeof the Braun tube, said smoothing means comprising at least condensersconnected on the one hand across the Wehnelt cylinder and the anode andon the other hand across the Wehnelt cylinder and the cathode of theBraun tube.

MANFRED VON ARDENNE.

